Compressional wave transmitting and receiving device



Nom 2, 1948. B. R. HUBBARD COMPRESSIONAL WAVE TRANSMITTING-AND RECEIVING DEVICE l Filed May 5, 1933 2 Sheets-Sheet l @gwdg/@Hubbard ATTORN the present invention.

-in the supersonic range in submarine listenihg nance in the compressional axes.

Patented' Nov. 2, IMS

UNITED STATES rENT.

`GOM'PRESSIONAI. WAVE TRANSMITTING AND RECEIVING -DEVICEI f Beverly R. Hubbard, Melrose, Mass., assignor, by

mesne assignments, to Submarine Signal Company, Boston, Mass., a corporation of 'Delaware Application May 5, 1933, Serial No.-669,477

are mined and afterwards cut for the purposes.

desired. In this group of crystals the present invention is concerned more particularly with the use of Rochelle-salt crystals whose piezo-electric eilect is more pronounced in general than crystals of other types. s

While vthe present invention is concernedwith the use o1' resonant and non-resonant crystals, I prefer to employ a resonant crystal resonant in the compressional axes. Crystals of this type are somewhat uncommon and prior to the present invention have never been generally used with resonant frequencies in the' range employed in I have determined that the most advantageous range of frequencies to use are those about. 'or Just above, the limit oi audibility, between the rangeof 20,000 to 40,000 cycles per second. Within this range the directive effect gained by the use oi aplurality of crystals operating together to produce a compressional wave beam balances or more than balances the natural attenuation of the high frequency in-,water so that the energy transmitted remains substantially at such a value that communication. signaling and soundings are easily accomplished.

In prior apparatus resonant crystals at this frequency have never been employed and in the present invention I have' devised methods by which resonant crystals of a composite of two or more crystals may be used which have a reso- Crystals of this type may be made by cementing similarly cut crystals together so that their compressional axes are aligned and the corresponding electric axes are parallel to one another.

In the present application the resonance of the structure may be broadened or narrowed, ole-- pending upon the loading which the crystals may have. In the present case the loading eiiected by the cover and the back plate is so chosen that the range covered is between 20,000 and 40,000 cycles. i

Further, in the present invention the crystals may be mounted on a heavy back plate and distributed radially about a central point or they may be mounted adjacent one another in a mosaic pattern.' Further, the exposed ends oi' the crystals may be in contact with a soft rubber cover or diaphragm, or they may be Just out of contact with such a cover and the space between them `and the cover filled with some liquid under v pressure equivalent to the external water pressure or under natural atmospheric pressure. Such liquid can be castor oil or some other suitable substance in which the crystal will not .be dissolved.

In the structures in which the crystals are grouped together the desired impedance may be obtained by connecting the crystals in proper series and parallel combination to produce the desired impedance in the circuit to which the receiver is connected.

For a voltage-operated device, such as a vacuum tube circuit, I prefer to use the crystals in a series combination in which by reason of the series combination the voltage generated will be high. In addition to this the receiver may preferably be connected directly into the grid circuit so that the impedance of the grid circuit, which can be made very high, will be properly matched.

When the apparatus is to be used in connection with a vacuum tube circuit in which the input between the receiver and the -circuit is effected V through a transformer, it is preferable either to use a parallelly connected combination of the crystals or a parallel series combination in matching the circuit impedance.

It -should be noted that the present receiver is a directional receiver particularly lbecause oi the dimension of the receiving surface as compared with the wave length of the Wave to be received in the compressional medium. Other 4than this, it should be noted that it is a pressure type of receiver and but for the directional eiec't gained through the large dimension of the receiving surface with lthe wave length of .the compressional wave it will receive as well from a direction at an anglevto -the normal as in the direction of vthe normal itself. A single crystal, therefore,

may be used as a non-directional receiver while the plurality of crystals associated together may be used as a directional receiver.

The present invention will be more fully described in connection wtlh :the drawings illustrat ing the invention in which Fig. l shows a' comm posits crystal formed of a plurality of crystals; Fig. 2 shows a plan view of a crystal receiver or .transmit-ter having a group of crystals mounted to form a number of rows; Fig. 3 shows a secn tional view along the line 3-3 of Fig. 2; Fig. 4 shows a plan view of a modification `of the device shown ln Fig. 2; and Fig. 5 shows a sectional view along the line 5 of Fig. 4.

In Fig. 1, as has been explained above, the composite crystal l may be formed bythe use of proper cement between the individual crystals. In an elongated crystal having the compressional axis a tuned to the desired resonant frequency within the receiving range of 20,000 to 40,000 cycles, the resonance may be made very sharp by using the crystal as a longitudinally freely oscillatins structure.

The compressional axis of the crystal is the axis in which'the greatest elongation and contraction take place. This axis is at an angle of 45 degrees to the so-called B and C axes which form with lthe A axis the three perpendicular axes of the crystal. If a crystal is cut in a rectangular pclyhedral form with the longer sides parallel to the i3 and C axes, the compression-al axis, so-called, will be defined as at 4an angle of 45 degrees to the B or C axis and perpendicular to the A or electric axis. If a potential ls applied between .the opposite surfaces at the ends of the A or electric axis and the crystal is held at one end .along a direction parallel to the B or C axis, the crystal at the free end will movein a direction parallel to the axis that is held. It is obvious from 4this that the maximum elongation and contraction will occur diagonally across the crystal, and, therefore, if thev crystal is cut diagonally at an angle of 45 degrees to the B and C axes, the compressional axis will be parallel to the polyhedral axis of the crystal in its cut form .and perpendicular -to the electric axis. It is this axis, therefore, that is called by the applicant the compressional axis.

In this case the electrodes 2 and 3 may be used either for applying alternating current poten-tial of the. desired frequency to vibrate the crystal at its resonant point or to receive .the electric variations due t-o the compressional waves applied in the' longitudinal axis Aa, of the crystal. The, crystal may be supported at its nodal position by the supports il and 5 and in order to broaden the resonance of' the crystal itself, the ends oi the crystal may be loaded or made of larger dimensions so as Ito produce the proper damping effect. Such a 4damping may be made to produ-ce a receiving or' transmitting structure having a resonance band of from 10,000 .to 20,000 cycles in width and preferably extending ibetween 20,000

. on a base plate i0 which may be provided with grooves il, I2, I3, it. I5, i6 and Il to Ireceive the rows ,of crystals I3, I9, 20, 2l, 22, 23, 2li and 25. At opposite ends of each row of crystals there are provided spring plates 26, 26 which not only t tend tc hold-the crystals in positiombut also serve to take on or supply the electrical energy to the apparatus.

The spring plates are supported at the sides of .the casing Aby means oi' the screws 21,21. 'llheI base plate i0 and the side of the casing 2B may be made of the same piece of material and prei'- erably is of some non-conductive hard material such as Bakelite, fl'ber or the like. `Between successive crystals are placed electrodes 29,' 29 and' v the crystals are so arranged that successive electrodes are positive and negative in the rows in l the same manner as a connection for a series of nected together and to the energizing terminalsv by means of the leads Il and 18. The rows I8, i9, 24 and 25 are series connected as illustrated. This circuit is tra-ccd as follows: the lead 18, crystal row 25, connector 82, lead 15, crystal row 24, connector 33, lead 8l, crystal row I9. connector and lead 13. crystal r-ow I8, lead 14,to the power supply. In this manner the apparatus may be connected in a series parallel combination in which there are three sets of 28 crystals in series. By varying the connections this, of course, may be altered and it is possible not only to connect all of the crystals in series, but 'it' is also possible to connect all of the crystals in parallel.

A parallel connection of crystals is most advantageous with a circuit having a comparatively low input impedance. 'Ihe lseries connection is preferable in a circuithavlng a high input impedance. The series connection in 'the 'present invention is preferably used when the crystals are directly connected in a grid circuit of a vacuum tube having a very high grid impedance and the parallel connection is preferably used in the present invention when .the device is connected to an amplifier or ya'cuum tube receiving circuit through a transformer or impedance coupling.

In the structure shown in Fig. 3 the plate I0 is provided with a ange 3| through which the screws 32 pass threading into the casing 33. In this type of construction the entire crystal units may be removed by unscrewing the screws 32 and removing the plate i0 which comes out of the back of the casing after the cover 34, held to the casing by means of the screws 35, has been removed. The front open end of the casing may be covered by a soft rubber cover or diaphragm ,36 which is preferably thin and acts primarily as a means of transmitting the compressional waves from theexternal medium to the crystals themselves. The diaphragm or cover 36 is heldin place through the clamping flange 31 which is clamped between the side Wall 28 of the plate IU and the casing 33. Any other suitable method for clamping the diaphragm 36 may be used 'and in order `thereby to remove the casing 28, it may be preferable to clamp the diaphragm 36 externally by means oi.l a clamping ring which holds the diaphragm -36 to the casing 33. By cutting in the face of the casing 33 this clamping ring may be made ilush with the surface -of the casing so that no material protrudes beyond the continued surface of the vessel which is indicated by the nufmber 8B, 38

Vsarcasm l,

just beyond the heavy clamping ring 89.

In the modification shown in Figs. 4 and 5 the casing 83 is provided with a rubber diaphragm corresponding to the diaphragm 36, in Fig. 3.

'Ihis diaphragm is held in position by means of the internal clamping ring lil` clamping the dlapliragmv to an inwardly extending ange in the casing 33.

The crystals 42, 42, as indicated more clearly in Fig. 4, are mounted radially about the center of the device upon a back plate d3 which is held to the casing 33 by means of the screws 4d. As indicated in Fig. 5, at the center of the plate 43 is an inwardly extending boss 4-5 which may be made of the same piece as the plate 43 or may be made of plate 43 by means of the screws 46. The piece 45, as indicated in Fig. 4, has cut-out portions 41 in which the edges of the ends of the crystals are positioned. Similarly a ring 48 held to the plate a separate piece, as shown, and held to thel 43 by means of the screws 49 is cut out at placesv 50 so that the crystals may be positioned by means of the inner piece and the outer ring 48 to prevent them from sliding radially in the structure. The crystals are also held in position from side-way motion by means of the electrodes 5I and 52 which furnish a support at the sides of the crystal, as indicated in Fig. 5, as Well `as serving as the electrical connections for conducting the current to the crystal or acting as the receiving electrodes.

The cable 53 connecting the apparatus, as .indlcated in Fig. 5, comes through the center of the plate 54 through a stuillng box 55 to make the internal chamber of the apparatus watertight.- The plate 54 is fastened to the casing 33 by means of the screws 55.

A tapped opening in the cover, closed by a plug 5B, provides means whereby the interior of.

the casing may be filled with a liquid such as castor oil or other liquid substance in which the crystals will not dissolve, in which case it is not necessary to'have the diaphragm 40 in contact with the ends of the crystals. Otherwise in order to have conduction to the external medium, the crystals should be in contact with the soft rubber cover. As has been previously mentioned, means may be provided in which the liquid within the casing may be put under lthe pressure corresponding to the external water pressure. However, merely lling the casing with a liquid has proved to be sullcient for ordinary purposes.

In the operation of the device the apparatus may be installed in the skin of a vessel or it may be used in sounding systems whereby it may be preferable to install it at the bottom of a vessel or have it so that it may be projected through a tube in the vessel itself. It is also possible to use this arrangement for direction finding anddirectional transmission in which case the oscillator shown in Figure 2 is used with its surface in a vertical Iorinclined position, and means are provided for rotating the device about a vertical axis to receive or transmit compressional iwaves in the desired direction. In order to use such an arrangement for projecting compressional wave beams downward, it is possible to provide the apparatus with a transverse or horizontal pivoted axis. This is easily accomplished by constructing the casing with two bearings at opposite ends of the diameter and pivotally supporting in a forked bearing-the oscillator in this position. By means of an arm extending from the ,top part of the casing the surf-ace of the oscillator may be inclined ,or tilted into the desired-position.

When used as a directional receiver or transmitter in the range of 20,000 to 40,000 cycles itis preferable to make the active diaphragm area of the oscillator large and many times the wave length. ,For this purpose it is satisfactory to have the active surface ofthe oscillator oi a diameter of approximately ten inches.

Having now described my invention, I claim:

1. An acoustical apparatus comprising in combination a. housing provided with a -face for the transit of acoustical energy, electromechanical interch'anging means positioned within said housing, said means including a plurality of vibratory Rochelle salt crystals, each of which is provided with end surfaces perpendicular to its compressional axis, and means in said housing supporting said crystals at points on opposite side surfaces,l said means maintaining said crystals in spacedapart relation.

2. An acoustical apparatus comprising in combination a housing provided with a face for the transit of acoustical energy, electromechanical interchanging means positioned within said housing, said means including a plurality of vibratory Rochelle salt crystals, each of which is provided with end surfaces perpendicular to its compressional axis, a supporting element in said housing, and recesses in said supporting element shaped to conform with individual crystals, said crystals being disposed in said recesses to be thereby sup-V ported by said element at points on opposite side surfaces.

3. An acoustical apparatus comprising in combination a housing provided with a. face for the transit of acoustical energy, electromechanical interchanging means positioned within said housing, said means including a plurality of vibratory Rochelle salt crystals, each' of which is provided with end .surfaces perpendicular to its compressional axis, a base plate in said housing for supporting said crystals, and raised portions on said `ment contacting each crystal on other side surfaces.

5. `An acoustical apparatus comprising in combination a housing provided with a face for the transit of acoustical terchanging means positioned within said housing) said means including a plurality or' vibratory Rochelle salt crystals, each of which is provided with end surfaces perpendicular to its compressional axis, a pair of concentric circular supportingelements in said housing, said crystals being each radially disposed between said elements, said elements contacting said crystals at opposite side surfaces.

6. An acoustical apparatus comprising in combination a housing provided with a face for the .transit of acoustical energy, electromechanical interchanging means positioned within said housing, said means including a 'plurality of vibratory Rochelle salt crystals, each of which is provided energy, electromechanical in-v aasaero REFERENCES CTED The following references are oi record. in the file of this patent:

UNITED STAZIES PATENTS Number Name te 1,450,246 Cady Apr. 3, 1923 1,495,429 Nicolson May 27, 1924 Number Number Name Date Perrin et al Sept. 22, 1925 Taylor Apr. 20, 1926 Taylor Apr. 20, 1926 Nicolson Jan. 10, 1928 yWilliams Aug. 28, 1929 Rice June 11, 1929 Nicolson Nov. 26, 1929 Nicolson Jan, 28, 1930 Nicolson June 24, 1930 Sawyer Apr. 28, 1931 Thomas Nov. 17, 1931 Tillyer -Sept. 5, 1933 FOREIGN PATENTS Country Date Great Britain July 28, 1921 Great Britain 1--- Mar. 8, 1928 Great Britain Dec. 4, 1930 

